Computing devices, such as notebook computers, personal data assistants (PDAs), kiosks, and mobile handsets, have user interface devices, which are also known as human interface devices (HID). One user interface device that has become more common is a touch-sensor pad (also commonly referred to as a touchpad). A basic notebook computer touch-sensor pad emulates the function of a personal computer (PC) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. A touch-sensor pad replicates mouse x/y movement by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touch-sensor pad itself. The touch-sensor pad provides a user interface device for performing such functions as positioning a pointer, or selecting an item on a display. A touch-sensor pad may also include buttons that permit a user to select items on a display or send other commands to the computing device such as a mobile handset.
A mobile handset (e.g., a cell phone) has a limited area in which buttons may be disposed. As illustrated in FIG. 1, the buttons in a mobile handset may be close to each other such that one touch by the finger of a user may trigger two buttons: a button desired to be pressed (e.g., button 1) and an unintended button (e.g., button 2). This issue often happens when a user inputs character or number quickly.
Some touch pads or buttons that have a capacitive sensor may utilize a capacitive sensor relaxation oscillators (CSR) to measure capacitance in terms of raw counts (e.g., the higher the capacitance the higher the raw counts determined by the CSR) during periods of oscillation. FIG. 2 illustrates the raw counts of eight buttons on the mobile handset of FIG. 1. When a user touches one button (e.g., button 1), other close buttons can sometimes be unintentionally triggered (e.g., button 2, button 4 and button 5). Such a “miss triggers” of unintended button activation is shown with straight arrows in FIG. 2. One solution to addressing miss triggers of buttons is to enlarge the distance between adjacent buttons. However, such a solution may reduce the button area and sensitivity of the device.